Optimisation Of Specific Draft Requirement And Hitch Length For An Animal-Drawn Sub- Soiler: A Case Study Of Sandy Clay Loam Soils

Abstract

Land degradation is occurring very rapidly in agricultural lands in Kenya. In ASAL regions, soil compaction and poor tillage practiced has resulted in increased cost of tillage, lack of timeliness and decreased agricultural production. The objective of this study was to optimize tillage depth and hitching length for optimal draft requirement in sandy clay loam soils. Parameters pertinent to draft requirement for subsoiling were identified. Field experiments were conducted to collect soil resistance datasets. Draft data was measured using the MSI 7300 digital dynamometer communicating remotely with data logger MSI -8000 RF logging data directly to a laptop through the serial port. The sub soiler tine tested was attached to a tool carriage attached to the oxen using a chain. The dynamometer was attached between the tool carrier and the oxen via steel shackles. For a specified speed, three hitch lengths (L1, L2 and L3) and three depths (D1, D2 and D3) were used in combination. Depth was measured as the vertical distance from the top of the undisturbed soil surface to the equipment deepest penetration depth and was varied from 0cm to 30cm with a range of 10cm interval. For each set up, three replications were performed giving a total of 27 treatments for each experimental site. Specific draft was evaluated at varying depth of 0-10cm, 10-20cm and 20- 30 cm and varying hitching length of 2.5m, 3.0m and 3.5m for each depth. The soil-resistance datasets obtained from the field tests were compared using statistical measures of fit particularly the coefficient of determination (R2) and the student t-test. At the experimental fields, the bulk density varied from 1.52 to 1.37g/cm3 and 1.44 to 1.67g/cm3 for Machakos and Kitui sites respectively. The moisture content increased with increase in depth at the two experimental sites ranging from 3.53 to 9.94% for Machakos site and from 4.15 to 9.61% for Kitui site Soil shear strength parameters ranged between 21.71 and 29.6kPa between depths of 0-20cm and then decreased to 28.07kPa for Machakos experimental site. In Kitui experimental site, shear strength parameters ranged between 30.02 and 39.29kPa between depths of 0 and 30cm. The relationship obtained between specific draft and depth at particular hitching length as well as specific draft against hitching length is a second order quadratic model of the form y = ax2 + bx + c. vii Currently majority of farmers in ASAL where Animal draft power is used extensively, the hitch length used is 2.5 m. However, from this study the optimal hitching length and tillage depth for Machakos experimental site was obtained as 2.9m (~3m) and 16.5 cm respectively. In Kitui experimental site, the optimal hitching length was obtained as 2.9 m (~3m) and the optimal tillage depth was 15.4 cm. In conclusion, this study has established that, for an animal drawn subsoiler, the optimal hitch length is 3m, which generates an optimal tillage depth in the range between 15 cm and 17cm at a minimum specific draft ranging between 32 to 35kN/m2 and 44 to 48 kN/m2 respectively in a sandy clay loam soils. Key Words: Soil resistance; optimal specific draft; hitching length; subsoiling depth; Animal draft power, Optimal hitching length, Optimal subsoiling depth, Agricultural mechanization, Kenya.